PRESIDENTIAL ADDRESS. 685 



energy cannot be obtained from nothing. This Testoration proces.s is effected 

 by an independent oxidation reaction, in which carbohydrate is burnt up with the 

 setting free of energy which is made use of to restore the muscle to its original 

 state. Confining our attention for the moment to the initial, contractile, stage, 

 the essential fact is the production of a certain amount of energy of tension, 

 which can either be used for the performance of external work or be allowed 

 to become degraded to heat in the muscle itself. It was Blix who first propounded 

 the view that the amount of this energy of tension is related to the magnitude of 

 certain surfaces in the muscle fibres. But the fact was demonstrated in a 

 systematic and quantitative manner by A. V. Hill. He showed, in fact, that 

 the amount of energy set free in the contractile process is directly related to 

 the length of muscle fibres during the development of the state of tension. In 

 other words, the process is a surface phenomenon, not one of volume, and is 

 directly proportional to the area of certain surfaces arranged longitudinally in 

 the muscle. This same relationship has been shown by Patterson and Starling 

 to hold for the ventricular contraction of the mammalian heart and by Kosawa 

 for that of the cold-blooded vertebrate. It appears that all the phenomena 

 connected with the output of blood by the heart can be satisfactorily explained 

 by the hypothesis that the energy of the contraction is regulated by the length 

 of the ventricular fibres during the period of development of the contractile 

 stress. The degree of filling at the moment of contraction is thus the determining 

 factor. 



That surface tension itself may be responsible for the energy given off in 

 muscular contraction was first suggested by Fitzgerald in 1878, and it seems, from 

 calculations made, that changes at the contact surface of the fibrillae with the 

 sarcoplasm may be capable of affording a sufficient amount. The difficulties in 

 deciding the question are great, but, in addition to the facts mentioned, there is 

 other interesting evidence at hand. It has been shown, by Gad and Heymans, 

 by Bernstein and others, that the contractile stress produced by a stimulus 

 has a negative temperature coeflicient. Within the limits of temperature between 

 which the muscle can be regarded as normal, this stress is the greater the lower 

 the temperature. The same statement was shown by Weizsiicker (working with 

 A. V. Hill) to hold for the heat developed in the contractile stage. Now, of all 

 the forms of energy possibly concerned, that associated with phase boundaries 

 is the only one with a negative temperature coefficient. Another aspect of this 

 relation to temperature is the well-known increase of the tonus of smooth muscle 

 with fall in temperature. 



It is tempting to bring into relation with the change in surface tension the 

 production of lactic acid. In fact, this idea was put into a definite statement 

 by Haber and Klemensievich in 1909 in a frequently quoted paper on the forces 

 present at phase boundaries. The production of acid is stated to alter the 

 electrical forces at this situation. This electrical charge involves a change of 

 surface tension, and it is this change of surface tension which brings about 

 the mechanical deformation of the muscle. Mines also has brought forward 

 good evidence that the production of lactic acid is responsible for the change of 

 tension. As to how the lactic acid is set free, and of what nature the system 

 of high potential present in muscle may be, we require much more information. 

 The absence of evolution of carbon dioxide when oxygen is not present shows 

 that no oxidation takes place in the development of tension. There are other 

 difficulties also in supposing that this .system present in resting muscle is of a 

 chemical nature. If the energy afforded by the oxidation of carbohydrate in the 

 recovery stage is utilised for the formation of another chemical system with high 

 energy content, the theory of coupled reactions indicates that there must be 

 some component common to both systems. It is difficult to see what component of 

 the muscle system could satisfy the conditions required. On the whole, some 

 kind of system of a more physical nature seems the most probable. It it be 

 correct that the oxidation of substances other than carbohydrate, fat for example, 

 can afford the chemical energy for muscular contraction, as appears from the 

 results of metabolism experiments, a further difficulty arises in respect to a 

 coupled reaction. But the question still awaits investigation. 



On the whole, I think that we may conclude that more study of thei phenomena 

 at phase boundaries will throw light on many problems still obscure. It would 



